docs: def get_all_choices(cls, *args, **kwargs):
          """
          Validate (template), de-duplicate (by template), sort (by label) and
          return a list of ``(template name, label)`` choices for all plugins.
          """
          plugins = cls.get_plugins(*args, **kwargs)
          all_choices = reduce(operator.add, [
              plugin.choices for plugin in plugins
          ])
          choices = []
          seen = set()
          for template, label in all_choices:
              # De-duplicate.
              if template in seen:
                  continue
              seen.add(template)
              # Validate.
              try:
                  validators.template_name(template)
              except ValidationError:
                  continue
              choices.append((template, label))
          # Sort by label.
          choices = sorted(choices, key=lambda a: (a[0], a[1]))
          return choices